Heat treatment of metallic strip material



Sept. 19, 1967 R. F. J. MORGAN HEAT TREATMENT OF METALLIC STRIP MATERIALFiled Oct. 15, 1964 ATTQRNEV INVENI'OE E. F. J Morgan United StatesPatent 3,342,649 HEAT TREATMENT OF METALLIC STRIP MATERIAL RobertFrederic Jenkin Morgan, Stockton-on-Tees, England, assignor to Davy andUnited Engineering Company, Limited, Yorkshire, England Filed Get. 13,1964, Ser. No. 403,567 Claims priority, application Great Britain, Oct.29, 1963, 42,575/63 8 Claims. (Cl. 148-16) This invention relates to theheat treatment of elongate material and particularly to means forimproving the rate of heat transfer from or to the elongate material.

In a previous arrangement for cooling elongate metallic material in theform of strip, the hot strip is passed between a plurality of coolinggas streams directed towards the strip surfaces.

With this arrangement it has been found that a laminar sub-layer of thecooling gas exists over the surface of the strip, and to some extent,this insulates the strip from the main turbulent flow of the coolinggas, thus reducing the rate of heat transfer between the strip and thegas.

The present invention provides a method of heat treating elongatemetallic material in which a stream of particulate material entrained ina gas at a different temperature from that of the material is directedtowards the surface of the travelling material. With this arrangementthe inertia of the particles of entrained material cause them topenetrate and break up the laminar sub-layer of gas, thus improving theheat transfer coefficient between the gas and the material.

The stream of entrained particulate material may have a component ofmotion in a direction opposite to that of the travel of the strip.

Apparatus for carrying out the method according to the present inventionmay include, a container through which the strip is passed in asubstantially vertical direction, means to provide a stream ofparticulate material entrained in a gas and directed towards the surfaceof the strip, means to withdraw the particulate material from thecontainer, and means to exhaust the gas from the container.

The following description relates to the accompanying drawing whichshows, by way of example only, apparatus for cooling metallic strip.

In the drawing, a container 11 has an inlet 12 through which steel strip13 passes horizontally into the container, and over a guide roll 14 topass upwardly and out of the container via an outlet 15.

A compressor 16 driven by a motor 17 supplies compressed nitrogen at apressure of about 10 lbs/sq. in. via an outlet 18 to a series ofmanifold pipes 19 suitably arranged adjacent the container 11. Thesupply lines from the compressor 16 to the manifold pipes 19 are omittedfor clarity.

Hoppers 20 containing sand at an average particle size of 250 microns,though the size may vary over a wide range, are connected by pipes 21 tosupply sand to each jet pipe 22 connected to an associated manifold pipe19. Nozzles 23, of the jet pipes, extend across the width of the stripand are inclined in a direction opposing the motion of the strip, sothat the streams emitted from the nozzles have a component of motionwhich is opposite to the direction of travel of the strip. The sand togas ratio is about l:2.

A plate 24 is provided above the roller 14 and the horizontal portion ofthe strip to prevent the sand particles falling on to the roller 14 andthe horizontal portion of the strip within the container, and sobecoming trapped between the roller and the strip.

An outlet 25 conveys the sand to an ejector 26, the primary nozzle 27 ofwhich may conveniently be supplied with nitrogen from the compressor 16to transmit the sand via a pipe 28 to a cyclone separator 29. The sandis returned to the hoppers 20 via pipes 30, and the nitrogen is returnedto the inlet of the compressor 16 via a pipe 31 and the hot-pass of asuitable heat-exchanger 32.

A suitable cooling fluid is circulated through the cold pass of theheat-exchanger 42 via an inlet 33 and outlet 34.

A magnetic separator 35 having a permanent magnet therein, is providedto separate scale from the sand withdrawn from the container 11.

In operation the streams of entrained sand from the nozzles 23 penetrateand break up the laminar flow of nitrogen over the surfaces of the stripand reduce its insulating property, thereby increasing the rate of heattransfer from the strip to the main body of cooling nitrogen.

The ejector 26 and the pipe 28 are arranged to convey away from thecontainer 11 the same quantity of nitrogen and sand as is admitted tothe container by the nozzles 23.

The increase in the heat transfer coeflicient using the method of theinvention as compared with ordinary jet cooling is about and in additionit is more economical in its use of machinery such as fans and blowers,since the required gas mass flow is less.

If the arrangement according to the invention is used in associationwith a steel plant having an oxygen tonnage plant, the surplus liquidnitrogen from the oxygen plant can be used to provide the nitrogen gasfor cooling the strip. In this case the nitrogen from the cyclone 29 maybe exhausted to atmosphere and the heat. exchanger 32 may be dispensedwith.

If the method according to the invention is applied to the cooling ofrod, then an arrangement as shown in our co-pending application 6,618/63 may be modified to pro vide annular jets in the wall of the duct 14,through which annular jets, the streams of particulate materialentrained in the nitrogen gas may be directed towards the surface of therod 12.

I claim:

1. In the method of continuously heating elongate metallic stripmaterial wherein the heated material is passed between a plurality ofcooling gas streams directed against the strip surfaces and having acomponent of motion opposite to that of the motion of the strip, theimprovement which comprises projecting with said gas a particulatematerial entrained therein which will penetrate and break up any laminarsub layer of gas which forms adjacent the strip surface thus improvingthe heat transfer coefiicient between the gas and the material.

2. A method as claimed in claim 1 which comprises continuously passingthe strip between a plurality of nozzles, while continuously directing astream of said particles entrained in said gas, at a lower temperaturethan that of the strip, through the nozzles towards the strip.

3. A method according to claim 1 in which the elongate metallic materialis steel.

4. A method according to claim 1 which. includes separatin g from oneanother the particles and gas which have been used to heat treat themetallic material, and con- References Cited tinuously recycling theparticles and gas. UNITED STATES PATENTS 5. A method according to claim4- which includes pass- 2,772,540 12/1956 Vierkouer X ing the gasthrough a heat exchanger- 5 3,116,788 1/1964 Beggs et a1 266-3 X 6. Amethod according to claim 4 which includes pass- 3,181,977 5/1965Sturgeon 148 -13.1 ing the particles through a magnetic filter to filterout 3,197,346 7/1965 Munday l4813.1 X scale FOREIGN PATENTS 7. A methodaccording to cla1m 1 1n whlch the partrcles 10 732,101 6/1955 GreatBritain.

are Sandv 906,349 9/1962 Great Britain.

8. A method according to claim 1 1n whlch the gas is nitrogen. CHARLESN. LOVELL, Primary Examiner.

1. IN THE METHOD OF CONTINUOUSLY HEATING ELONGATE METALLIC STRIPMATERIAL WHEREIN THE HEATED MATERIAL IS PASSED BETWEEN A PLURALITY OFCOOLING GAS STREAMS DIRECTED AGAINST THE STRIP AND HAVING A COMPONENT OFMOTION OPPOSITE TO THAT OF THE MOTION OF THE STRIP, THE IMPROVEMENTWHICH COMPISES PROJECTING WITH SAID GAS A PARTICULATE MATERIAL ENTRAINEDTHEREIN WHICH WILL PENETRATE AND BREAK UP